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Old 09-29-2011, 08:54 AM   #1
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Custom Exhaust questions/ Help Please

So has anyone removed their cat when doing a custom exhaust?

I have a 98 TJ SE (2.5 5-spd) that i want to do an exhaust on but i HATE cat's (the animal kind too ) and want to remove it but when i looked at it there is an O2 sensor between the cat and muffler which i dont know what to do with.....I was thinking cut exhaust pipe before cat and after muffler then remove both with 02 sensor between them and the cut O2 sensor section out and weld in after the new muffler??? would this cause problems to how the sensor reads and mess up how the engine runs?
Thanks! Nick

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Old 09-29-2011, 08:58 AM   #2
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Unless you don't plan on registering the jeep again for road driving-you cannot remove the CAT without violating Federal law and state emission rules...and yes, removing it will screw up your sensors and computer...

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Old 09-29-2011, 09:46 AM   #3
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A healthy, decent quality, cat doesn't really have any negative side effects. I can't think of a reason to hate one. I can't think of a reason to hate anything.
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Old 09-29-2011, 09:55 AM   #4
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That O2 sensor behind the CAT compares emissions with upstream sensor to make sure you have the CAT there. Your check engine light will come one if you remove it and you will never get an inspection sticker
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Old 09-29-2011, 10:17 AM   #5
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Ok, thats what i was wondering...hmmm well then maybe just replace/remove the muffler? i wonder how bad it would sound with out a muffler. I had a 90 f-150 with the 300 six in it and did a straight pipe exhaust (gutted cat and no muffler) and the thing was crazy loud, sounded cool at idle then like a tractor at the pulls when taking off...had to put a muffler on it.

and i guess i dont HATE them i just dont like them...and animal cats i dont hate them either just would rather have outside only animals.

Thanks for the replies guys maybe i'll just slap a muffler on it....i dont know
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Old 09-29-2011, 12:08 PM   #6
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Unless you don't plan on registering the jeep again for road driving-you cannot remove the CAT without violating Federal law and state emission rules...and yes, removing it will screw up your sensors and computer...

That O2 sensor behind the CAT compares emissions with upstream sensor to make sure you have the CAT there. Your check engine light will come one if you remove it and you will never get an inspection sticker

Another case of people opening there mouth and speculating!!!
Have you two done this? Then how do you know? Deductive resoning or you just fawking guessed!

I HAVE done this and yes it works just fine on my OFF ROAD ONLY TJ that DOT can pound salt on.
No CEL whatsoever.
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Old 09-29-2011, 01:37 PM   #7
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My buddy has a cherokee with the same 4.0 I6 engine.
He has a cat, but cut out the muffler and straight piped it.
It sounds like garbage...i do not reccommend it if you want a decent tone out of your exhaust
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Old 09-29-2011, 03:42 PM   #8
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I agree, I ran my 4L with a dump right behind the cat for a while. Sounded great while under hard acceleration but wasn't so good for normal driving.
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Old 09-29-2011, 05:54 PM   #9
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It is not going to screw up sensors or set off a CEL. Removing a cat has always been taboo on jeep forums and I a'm not saying to remove it but it is done on other types of vehicles plenty. Depending on your local inspection process, it may not matter as far as registration.
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Old 09-29-2011, 08:10 PM   #10
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its a 2.5l leave the stock exhaust or it will sound like a ricer. Jeeps that sound like ricers make me sad and not want to wave.
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Old 12-20-2011, 11:52 AM   #11
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I hollowed one out on one i had, put a glass pack on it and called it a day. Without it i thought it would sound like crap; however hollowing it added a deep sound. We don't have to worry about inspection here. (It never set off a sensor, nor had any ill effect!) although i had allot of people tell me it would...BS
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Old 12-20-2011, 12:00 PM   #12
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I've got a magnaflow cat and magnaflow muffler on my 2.5 and it doesnt sound bad at all...no fart can sound, not annoying, and really didnt change it up much from the stock sound...just opened it up more and gave it a slightly deeper pitch.
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Old 07-27-2014, 04:08 PM   #13
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Quote:
Originally Posted by tconners View Post
Unless you don't plan on registering the jeep again for road driving-you cannot remove the CAT without violating Federal law and state emission rules...and yes, removing it will screw up your sensors and computer...

That O2 sensor behind the CAT compares emissions with upstream sensor to make sure you have the CAT there. Your check engine light will come one if you remove it and you will never get an inspection sticker

Another case of people opening there mouth and speculating!!!
Have you two done this? Then how do you know? Deductive resoning or you just fawking guessed!

I HAVE done this and yes it works just fine on my OFF ROAD ONLY TJ that DOT can pound salt on.
No CEL whatsoever.
I for one HAVE done it on an 06 2.4 and the CEL came on before I put 90 miles on, I could clear it and it would keep returning, until I returned it to original configuration. In fact when I put a Magaflow cat back exhaust on it, it opened the flow up so much that it triggers the same error code. My next step is a mated Magnaflow cat, as supposedly it will cure this issue (per summit racing). So you seem to be the one opening YOUR mouth based on YOUR LIMITED experience on one model year and PCM revision code.
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Old 07-28-2014, 06:20 PM   #14
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I did a custom flowmaster exhaust on my 97. I left the cat on and put the flowmaster super 44 muffler on and it sounds amazing. Very throaty and not too loud. I know without a cat on with this muffler it's very loud and can sometimes shoot flames depending. I wouldn't recommend removing the cat though.
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Old 07-28-2014, 08:15 PM   #15
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I have an 01 4.0 that I gutted the 2 precats and the cat. Sets off a check engine light about every 100 miles but will go away on its own if you do a couple short trips. I gave up on clearing the codes. I even put the stupid spark plug defoulers piggybacking the rear o2 sensors which works on every other vehicle I own (currently a silverado ss and an audi s4, along with about 10 other vehicles I've had in the past). I also hate cats, the animal cats and hippies. I just clear the code the month I need an inspection and wait for the the 4 out of 5 readiness stages of the ecu to be ready (in the communist state of NY surprisingly you can pass inspection with one stage "incomplete"). Even my old yj I gut the cats on and it never triggered anything but then again that wasn't OBD2...

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